The invention is directed to a method for driving a combustion motor which has a combustion chamber inside which a fuel is burned in cycles and from which the hot, pressurized combustion gas created during the combustion flows into an expansion chamber which is separate from the combustion chamber and where it moves a piston.
Furthermore, the invention is directed to a combustion motor which has a combustion chamber for the cyclical combustion of a fuel, during which a combustion gas is generated, and a separate expansion chamber which is connected with the combustion chamber via a controllable combustion chamber discharge valve and which provides a bearing for a piston that permits the movement of said piston so that the energy of the combustion gas can be converted into mechanical work or energy.
Such a method for driving a combustion motor and respectively such a combustion motor are already known from EP 0 957 250 A2. For this combustion motor, cooling water is sprayed into the expansion chamber at the end of the expansion phase when the piston is at its bottom dead center and when the combustion gas has relaxed to approximately atmospheric pressure. The low pressure caused by the sudden cooling of the hot combustion gases pulls the piston up towards its upper dead center while loading a spring. This stored energy is released to the piston during the next expansion phase when the piston is again moving from the upper to the bottom dead center. By means of spraying in a cooling liquid, the thermal energy of the hot combustion gases, which is normally discharged unused through the exhaust of customary motors without such an injection of cooling liquid, can be used to do work.
It is an important object of the invention to further improve the method of the type mentioned in the start while allowing a further increase of the efficiency of the combustion motor. According to the invention, this can be done by using a method for driving a combustion motor which has the following procedural steps:
cyclical burning of a fuel in a combustion chamber;
letting hot pressurized combustion gas created during the combustion flow into an expansion chamber separate from the combustion chamber where it moves a piston while expanding during an expansion phase; wherein at least for a partial load operation of the motor the combustion gas in the expansion chamber already reaches atmospheric pressure before the end of the expansion phase of the combustion gas; in consequence, the movement of the piston continues in the same direction of movement whilst the combustion gas in the expansion chamber expands further and pressure is generated that is below atmospheric pressure;
spraying cooling liquid into the combustion gas which is at subatmospheric pressure at the end of the expansion phase of the combustion gas; wherein the pressure of the combustion gas is reduced further and the subatmospheric pressure in the expansion chamber acts on the piston and the piston performs work under the effect of this subatmospheric pressure.
Such a thinning of the combustion gas to a value below atmospheric pressure before the implosion of the combustion gas by injection of a cooling liquid is effected has the effect of increasing efficiency; this is similar to the way in which compressing the air introduced into the combustion chamber before burning the fuel-air mix leads to higher efficiency compared to burning the fuel-air mix at atmospheric pressure. Preferably though, the pressure of the combustion gas in the expansion chamber should still be above 0.3 times atmospheric pressure immediately before the implosion phase.
In a preferred embodiment example of the invention, the compression of the air introduced into the combustion chamber is also implemented, wherein advantageously the piston is connected to the compressor piston of a compressor pump by means of a piston rod and the compression takes place during the upward movement of the piston from bottom dead center to upper dead center and is supported by the subatmospheric pressure in the expansion chamber.
The expression xe2x80x9cexpansion phasexe2x80x9d is used for that phase during the working cycle of the motor when the volume of the expansion chamber of the motor increases and the combustion gas therefore expands (either by itself or under the effect of a force). After the injection of the cooling liquid follows the xe2x80x9cimplosion phasexe2x80x9d during which the volume of the expansion chamber decreases while the pressure of the combustion gas increases again towards atmospheric pressure. After atmospheric pressure is exceeded, an xe2x80x9cexhaust phasexe2x80x9d follows during which the combustion gas is expelled from the expansion chamber. Preferably, this is to be followed by a xe2x80x9cwaiting phasexe2x80x9d of the piston during which fuel is burned in the combustion chamber and the piston preferably to be realized as a reciprocating piston stays in its upper dead center (OT). After the combustion of the fuel in the combustion chamber which advantageously would be complete, the next expansion phase is started.
A combustion motor with an expansion chamber separate from the combustion chamber for which the combustion gas during partial load operation of the motor towards the end of the expansion phase is at a value below atmospheric pressure is already known from U.S. Pat. No. 5,311,739. This effectxe2x80x94here as such unwantedxe2x80x94occurs because the volumes of the combustion chamber and the expansion chamber are determined by the gas volume during full load operation; during partial loads, subatmospheric pressure is therefore created towards the end of the mechanically forced piston travel. By means of the measures described in U.S. Pat. No. 5,311,739, the motor can still be operated in partial load operation, in spite of this subatmospheric pressure that is being generated.
A combustion motor is advantageously suited for the embodiment of the method according to the invention which has a combustion chamber for the cyclical combustion of a fuel during which a combustion gas is generated, and a separate expansion chamber which is connected with the combustion chamber via a controllable combustion chamber discharge valve and which provides a bearing for a piston that permits the movement of said piston so that the energy of the combustion gas can be converted into mechanical work or energy, wherein at least one injection nozzle is provided that opens into the expansion chamber for the purpose of injecting a cooling liquid to decrease the volume of the expanded combustion gas suddenly; and wherein at least one roller is arranged on the piston rod of the piston as a thrust-transmitting member of a cam gear; and wherein curved surfaces of this cam gear, active in both stroke directions of the piston, are resting on both sides of this roller.
By use of this cam gear active on both sides and connected to the piston rod of the piston, the thinning of the combustion gas before the start of implosion phase can be done in an easy manner by spraying in the cooling liquid. As long as the combustion gas in the expansion chamber is under pressure above atmospheric during the movement of the piston from upper dead center to bottom dead center, a thrust-transmitting member in the shape of a roller connected to the piston rod acts on the curved surface that is further away from the piston. As soon as the pressure of the combustion gas in the expansion chamber drops below atmospheric pressure, the curved surface that is closer to the piston acts upon this thrust-transmitting member while the downward movement of the piston is being supported and the pressure of the combustion gas in the expansion chamber falls below atmospheric pressure. The energy required for thinning the combustion gas is drawn from the kinetic energy of the system. This loss of energy, though, is more than compensated for by the fact that the pressure in the expansion chamber keeps on dropping further in the subsequent implosion phase after the injection of the cooling liquid than it would have done without such a thinning and that therefore more work is performed in the implosion phase during the travel of the piston from bottom dead center to upper dead center. This work done in the implosion phase can be transmitted via the cam gear directly to the shaft driven by the cam gear. In a preferred embodiment example of the invention, a compressor pump is driven by the piston during its upward movement. If the energy available during the implosion phase is not sufficient by itself to drive the compressor pump, kinetic energy is again withdrawn from the system by means of the cam gear. If on the other hand the power available during the implosion phase is above the drive power necessary for the compressor pump, the additional power is transmitted via the cam gear to the shaft driven by the cam gear.
A method for driving a combustion motor according to the invention or rather the combustion motor according to the invention are advantageously suited for operating the combustion motor at a partial load. For this, the combustion motor according to the invention can, for example, be realized in such a manner that the thinning of the combustion gas (=pressure drop to below atmospheric) before the start of the implosion phase does not happen during full load operation of the motor. If on the other hand it is operated at a partial load when smaller amounts of fuel and air are introduced into the combustion chamber, the combustion gas is thinned before the bottom dead center of the piston is reached. Because of the lower compression in the combustion chamber, the efficiency during the expansion phase drops while the efficiency during the implosion phase increases because of the thinning of the combustion gases. In all, a more balanced efficiency can be attained by means of this for the full and partial load operation of the motor.
A motor according to the invention that can be operated at full and partial load furthermore permits a much easier control of the combustion motor when compared with the combustion motor known from EP 0 957 250 A2. For the motor according to the invention, the motor control (control of the hydraulic valves and of the water and fuel injection) can be done by a simple cam action pump, since the hydraulic impulses (pressure impulses) must always happen within a defined segment of the rotation and no variable control times or variable rotation angles occur. Furthermore, the starting of the motor can be done in a simple manner by means of an alternator (=starter motor and generator in one) acting on the cam shaft, wherein the stroke of the compressor piston of the compressor pump is also forcibly started via the cam gear and the piston of the expansion chamber so that the necessary starter air pressure is charged in the combustion chamber without the need for a separate starter air pump.
For stationary engines constantly operated at full load, the thinning of the combustion gas according to the invention is provided for the full load operation of the motor before the implosion phase, but a thinning of the combustion gas before the start of the implosion phase can also be done advantageously for motors operated at both partial and full load when they are in full load operation.
The usable effect of thinning the combustion gas to a pressure below the surrounding atmospheric pressure before the start of the implosion phase is subsequently to be illustrated in two dimensioned examples for comparison. In both examples it is assumed that the expansion of the combustion gas, for example determined by a partial load of the motor, has progressed to atmospheric pressure after half the piston stroke of the expansion phase.
In the first sample case, the implosion is started after atmospheric pressure is attained in the expansion cylinderxe2x80x94the piston stroke is not executed all the way to bottom dead center. Therefore, the implosion can only have an effect during half of the stroke length (minus the partial distance for the exhaust stroke shortly before upper dead center). In the second sample case, the stroke is finished all the way to bottom dead center, which causes subatmospheric pressure in the expansion cylinder, and for which thinning work of the piston, work must be applied to this piston. The exhaust gas is cooled by the injection of the cooling liquid into the expansion cylinder at bottom dead center. Because of the subatmospheric pressure already existing before the implosion because of the thinning, the total subatmospheric pressure of the implosion reaches a lower value than in the first sample case without thinning before the implosion.
From the work capacity of this additional part of the pressure below the implosion pressure of the first sample case alone, the power added at the end of the expansion stroke for the thinning of the exhaust gas is approximately regained during the implosion stroke. The subatmospheric pressure of the implosion effective as work for compression and at the most partially effective as work given off to the outside remaining after this, now hasxe2x80x94in contrast to the first sample casexe2x80x94not only an effect during half the stroke length but during the entire stroke (minus the part for the exhaust stroke). The implosion power is therefore approximately doubled in the sample cases, meaning: when the preceding expansion phase is in the partial load range, the usable power from the implosion phase for the second sample case is approximately the same as it is when the preceding expansion phase is operated at full load.
From this furthermore follows: The most advantageous area for reaching atmospheric pressure of the combustion gas so that the thinning which is the object of the invention can be utilized is in the area around the middle of the piston stroke. If the state of the combustion gas of being at atmospheric pressure was attained close to upper dead center, the effort (work added) needed for thinning the exhaust gas until the bottom dead center is reached would increase out of all proportion when compared with the work to be gained from the subsequent implosion phase. If on the other hand the combustion gas were to reach atmospheric pressure close to bottom dead center, the thinning could barely take place through lack of further travel of the piston.